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Message-ID:  <000f01c292ae$19b8c720$0a00a8c0@dan>
Date:         Sat, 23 Nov 2002 00:06:37 -0500
Reply-To:     Dan DeConinck of PixelSmart <[log in to unmask]>
Sender:       ImageJ Interest Group <[log in to unmask]>
From:         Dan DeConinck of PixelSmart <[log in to unmask]>
Organization: PixelSmart
Subject:      need to de-interlace after switching to Jaguar

Hello,

Regarding your deinterlacing problem, I have comments but not a solution.

I believe the artifact you described is called feathering. ( Not sure of the
name )  You state a fact that many people are not aware of.  The odd and
even field ( which together compose what is called a frame ) are captured at
different moments in time. The impact of this is that when you look at one
frozen frame you are really looking at two images taken at two different
moments in tine.  If there is any motion between the moments in time when
the two fields were taken, then you get this artifact that you are seeing.

If a NTSC video player is written correctly then you will not notice this
artifact because it will not display the two fields at the same time. It
will play the fields one after the other in the same order that they were
captured. Thus on playback you do not see this motion artifact. If the
artifact does not show up in the quick time play, I would guess this is
because Quick Time is handling the task correctly. Its only when you freeze
two fields ( a frame ) and display then as one image ( which they are not )
that you see this arrtfact.

People who set out to design video software players and also video hardware
circuitry sometimes design in this artifact as they are not familiar with
the true nature of interlaced video. Its understandable that this artifact
is causing you trouble.

P.S. - If you watch the British open golf you will notice the ball
momentarily moving retrogade. ( during drives ) The 25 fps European video
gets incorrectly converted to the US 30fps standard. They need to repeat
fields to translate the 25 fps to the 30 fps. But they repeat frames instead
of fields which means they go back in time, instead of standing still in
time, as you would get with repeating a field.....  and so it goes.

Sincerely
Daniel DeConinck
www.PixelSmart.com
TEL: 416-248-4473

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